PJB-2019-932
Study on CO2 response process and the applicability of four mathematical models in leaves of two tree species under different soil water conditions
Wu Qin
Abstract
CO2 concentrations and soil moisture contents would affect tree growth and the physiological mechanisms. This study investigated the photosynthetic CO2 responses in the leaves of two-year-old Prunus sibirica L. and Hippophae rhamnoides L. under eight soil moisture conditions in the semi-arid loess hilly region. The CO2 response curves and parameters were fitted using a rectangular hyperbola model, non-rectangular hyperbola model, exponential equation, and modified rectangular hyperbola model, and the quantitative relationship between photosynthesis and soil moisture is discussed. The results showed that the relative soil water content (RWC) required to maintain a high photosynthetic rate (Pn) and carboxylation efficiency (CE) was in the range of 46.5%-81.6% for P. sibirica L., and 42.8%-83.2% for H. rhamnoides L..When RWC was outside the above ranges, the photosynthetic capacity (Pnmax), CE, and CO2 saturation point (CSP) of the two tree species decreased markedly. The CO2 response curves and parameters of photosynthesis such as CE, the CO2 compensation point (Γ), and the photorespiration rate (Rp) were well fitted by the four models when RWC were appropriate for the two tree species. The non-rectangular hyperbola model and the modified rectangular hyperbola model fitted the data were moderately good under appropriate RWC conditions. When RWC exceeded the optimal range, only the modified rectangular hyperbola model could well fit the CO2 response curves and photosynthetic parameters.
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